This invention relates generally to automatic knot-tying devices and more particularly to an automatic knot-tying device for tying a knot around a generally cylindrical target item.
In many industries, both military and commercial, such as the aircraft, automotive, and appliance industries, wire bundles, or harnesses, are used extensively in the manufacturing processes of various products. Each bundle, or harness, generally comprises two or more wires that customarily are tied together at various points along their lengths to help ensure safety and durability, as well as a generally clean design.
Individually tying the bundle points by hand is costly, labor-intensive, and time-consuming, and often leads to carpal tunnel syndrome, or other physical injury, in the operator. With these problems in mind, several patented inventions have been directed toward automating the wire-tying process. One such device, that described in German Offenlegungsschrift No. 2,533,640 and improved in U.S. Pat. No. 4,558,894 to Detterbeck et al, is a hand-held pistol-like apparatus that forms a continuous crocheted tying structure around and along a bundle of wires. Even Detterbeck""s improvement, however, does not actually tie a knot around the bundle: it simply pulls taut a predetermined number of loops. The device, therefore, is limited because it is not capable of tying individual knots at discrete points along the bundle.
Another patented device is described in U.S. Pat. No. 4,094,342 to Nishikawa et al. Nishikawa""s device uses guide channels along the inside surface of the bundle holding elements to guide the string or cord around the wire bundle into the shape of a knot. The string is then pulled taut and cut. Several problems, including jamming and inconsistent knot quality, are associated with the Nishikawa device because it pushes, rather than pulls, the string around the bundle.
One feature of knot-tying is that a second pass of the string around the bundle must be laid in front of or behind a first pass. The prior art has not dealt with this problem very successfully; instead, many prior art devices have tried simply to lay the string in patterns described by guide channels in the holding elements themselves. The Nishikawa device, and other devices, particularly the one described in U.S. Pat. No. 3,057,648 to Schwarze et al, use guide channels of differing depths to result in criss-crossing passes of the string. In a different approach, the device disclosed in prior art patent to Jung et al., U.S. Pat. No. 4,502,905, uses a transverse pin with a hook to grab the second pass of the string and draw it back across the first pass.
The device in U.S. Pat. No. 6,279,970 to Torres improves upon the other prior art devices by using a system comprising a nozzle and various reciprocating pins and hooks which move the string or other filament into and out of the knot-tying area. The Torres device pulls, rather than pushes, a string, cord or other filament (such as the FAA-approved xe2x80x9clacexe2x80x9d) around the workpiece, such string issuing from the nozzle, while the pins and hooks manipulate the string into the knot configuration. However, the Torres device is quite complex, having 25-30 motions involving rings, pins, and hooks, which must be precisely coordinated and indexed in order to accomplish the knot.
The Jung device illustrates another problem in the prior artxe2x80x94that of finishing the knot. After the string is laid around the bundle, the Jung device heats and bonds the string instead of tying a knot. Such heating, or other type of fusing or bonding, as well as the use of plastic, generic cotton string, or other fabric are frequently not acceptable because of the harsh environments encountered by many installations of wire bundles. Depending upon the particular industry and the application of the product, these bundles may be placed in environments of extreme temperature, vibration, radiation, or other types of shock. To withstand these conditions while maintaining the integrity of the knot, many applications require the use of xe2x80x9clace,xe2x80x9d a particular type of flexible string-like material.
The present invention is an improvement upon the device in Torres U.S. Pat. No. 6,279,970, because the present invention uses fewer moving parts and requires fewer steps to accomplish the tied knot. The present invention also improves upon the complexity of the Torres device by eliminating many coordinated motions. Further, it has the capability of tying many different types of knots, including the knot specified by aircraft manufacturers.
One aspect of the present invention comprises a compact, lightweight, hand-held housing with an activating button or switch (the device can be powered either electrically or pneumatically) so that a user can easily manipulate the device and apply a knot at any desired discrete location, or a series of discrete locations, along a wire bundle or other target item, that may be of circular, oval, rectangular, or other regular or irregular geometric cross-section. In this preferred embodiment, the housing defines a generally U-shaped opening into which the bundle fits with the bundle""s longitudinal axis orienting generally transverse to the housing""s handle, and to the reference plane defined by the U-shaped opening. The user does not have to manipulate the bundle or come into physical contact with it at all; he or she simply thrusts the device around the bundle and presses the button.
The housing contains a knot-tying mechanism that ties an actual knot, i.e., not loops or chains of loops, around the wire bundle, by pulling the tying filament (i.e., any flexible, generally cylindrical length of tying material), not pushing it as most prior art devices do. With the present invention, any of several different knots could be tied, with different arrangements and indexing of rings, shuttles, and hooks; however, in the preferred embodiment, it has been chosen to tie a clove hitch around the wire bundle and then tie a surgeon""s knot to secure the clove hitch, because this combination of clove hitch and surgeon""s knot is the FAA-approved method of tying wire harnesses. Military aircraft manufacturers also require use of the clove hitch/surgeon""s knot combination.
Further, the FAA (Federal Aviation Administration) and military specifications also often call for the use of xe2x80x9clace,xe2x80x9d a particularly durable type of braided filament. Although it can use a variety of filaments, the preferred embodiment of the present invention has been designed to use xe2x80x9clace,xe2x80x9d and the remaining discussion will use that term.
The preferred embodiment of the knot-tying mechanism operates in three distinct stages. In the first stage, the mechanism wraps and tightens the clove hitch around the bundle, and then in the second stage, the mechanism ties the surgeon""s knot to secure the clove hitch. In the third stage, the mechanism, after cinching and cutting the knot, resets itself for the next knot-tying operation. A continuous supply of lace, or other filament, is fed to the device by a belt-mounted or housing-mounted spool, or some other method.
The entire knot-tying process from the moment the device engages the bundle to the moment the device disengages the bundle, leaving a precisely tied, tight, and finished discrete knot, takes approximately 5 seconds, using the preferred embodiment. Of course, alternate embodiments, particularly with alternate controlling means, can easily modify the processing time, e.g., for other types of knots.
The knot-tying mechanism of the preferred embodiment comprises three C-shaped carriage rings for wrapping the lace (hence sometimes referred to as xe2x80x9cwrapping ringsxe2x80x9d) generally transversely around the wire bundle or other workpiece; a single shuttle, which shuttles between the rings (along an axis parallel to that of the workpiece), carrying the lead end of the lace with it, thereby laying the lace over or under the previous passes; and two hooks, which pull the lace away from the knot-tying area and form loops with the lace at appropriate times.
The preferred embodiment also comprises two clamps, one on either side of the knot-tying mechanism, for centering and stabilizing the workpiece within the working area of the mechanism. In the preferred embodiment, which is a hand-held embodiment of the invention, the clamps are sized to accommodate a generally cylindrical workpiece (e.g., bundle of wires) having a size range from xe2x85x9xe2x80x3 to 1xe2x85x9xe2x80x3 diameter. When the user first engages the preferred embodiment of the device with the bundle, by placing the opening of the housing generally transversely around the bundle, the clamps are activated. At this point, the knot-tying mechanism is in the initial set-up position. In this initial set-up position, the lead end of the lace issuing from the supply spool has been fed through a guide attached to one of the rings into the interior working area, defined by the C-shaped rings, and is being held in place by a clamp on the shuttle. Once actuated, by the button or other actuation method, the mechanism begins the clove hitch process. With the lace being continuously available from the supply spool through the guide, the carriage rings rotate around the bundle, carrying the shuttle and the lace with them. As the rings rotate around the workpiece, stopping at predetermined index positions, the shuttle carries the lead end of the lace back and forth between the rings. The two hooks, which are referred to in the preferred embodiment as the up hook and the down hook and are oriented in opposite directions away from the workpiece, come into play at various times to snag the lace. When the hooks have snagged the lace and are extended away from the workpiecexe2x80x94in their respective opposite directionsxe2x80x94a loop is formed in the lace. The cooperation and indexing of the rings, the shuttle, and the hooks result in the chosen knot being properly laid and tied around the workpiece.
Once the clove hitch is complete and tight, the knot-tying mechanism then ties and finishes a surgeon""s knot to secure the clove hitch and then finishes the procedure. In this surgeon""s-knot tying process, the same three carriage rings, shuttle, up hook, and down hook are used as were used in the clove hitch tying process.
In the preferred embodiment, once the surgeon""s knot is complete, the lace knot is tightened and a cutting edge severs the lace so that the knot is stand-alone and discrete. The subsequent lead end of the lace is then reattached to the clamp on the shuttle, and the mechanism is ready for the next application.